US3183896A

US3183896A - Separating heater

Info

Publication number: US3183896A
Application number: US337860A
Authority: US
Inventors: Robert I Lytle; George P Moran; William D Stevens
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1964-01-15
Filing date: 1964-01-15
Publication date: 1965-05-18
Anticipated expiration: 1982-05-18
Also published as: DE1426698B2; GB1054222A; DE1426698A1

Description

May 18,v 1965 R. l. LYTLE ETAL SEPARATING HEATER 2 Sheets-Sheet 1 Filed Jan. 15, 1964 wok IQMK mt know mvgNToRs RQBERrI. Yr/ E GEORGE P. HORA/V u//LL/AM D. .Sfvfws May 18, 1965 R. l. LYTLE ETAL i 3,183,896

SEPARATING HEATER Filed Jan. l5, 1964 2 Sheets-Shef-Jcl 2 Z. W2. 72 76 96 ,JEP/wn ro@ l! a ik A f c if 44 I N V EN TO R5 1908567 f. L Yraf:

6501965 R /Vo/PA/v W/B/AM 0. Sra/NS ATTORNEY United States Patent() 3,183,896 SEPTING MATER Robert I. Lytle, Morristown, George?. Moran, Basking Ridge, and William l). Stevens, North Caldwell, NJ., assignors to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Jan. 15, 1964, Ser. No. 337,860

6 Claims. (Cl. 122-466) This invention relates to a once-through subcritical or supercritical steam generator flow system, and in particular, to novel means for start-up, re-start and operation The lower enthalpy phase is circulated back to the steam t s generator through a deaerator and proper circuits.

To perform the two functions of uid separation and latent heat transfer, a start-up by-pass system, including a flash tank and a heatexchanger, is utilized representing a substantial investment in 4two high pressure` vessels and `associated components. A f

It is an object of the invention to perform the forementioned functions within a single vessel, hereinafter called a separating heater, in a novel and facile manner which will provide a greater heat recovery and will represent a lower capital investment for the required functions.

The invention provides means for separating the twophase fluid into its basic components and at the same ,time provides means by which the latent heat of the high enthalpy fluid is transferred to the incoming feefwater. In addi-tion, the low `enthalpy iiuid is handled within the separating heater and is transferred back to the cycle. Thin-in effect, allows for a better heat recovery within the cycle obtaining a minimum loss of start-up heat input and logically a minimum start-up time.

Also providedin accordance with the invention is a means to direct the high enthalpy fluid to the turbine :gland seals, deaerator, and to the turbine forr'early-rollv ing once the point is reached when the incoming steam quantity exceeds the latent heat absorbing capabilityof the heat exchanger. A secondary means of separating any possible undesirable quality from this high enthalpy fluid is provided as an embodiment in accordance' with the invention.

VThe latent heat absorbing capacity of the separating heater is controlled by means of a by-pass of the incoming feedwater, in order to deliver the high enthalpy luid sooner to the turbine for warming up and early rolling.

It i-s a further feature ofthe invention to provide a means for transferring heat to the incoming feedwater during normal operation, that is', when the start-up by- Y pass system is taken out of service. This is accomplished in 'accordance with the invention by making use of the `desuperheating, condensing, and sub-cooling surfaces in the separating heater for transferring heat lfrom highenthalpy intermediate turbine bleed fluid to feedwater.

These objects and advantages of the invention will become apparent upon consideration of the specification and accompanying drawings, in which: FIGURE 1 is a flow diagram `for a once-through steam generator in accordance with the invention;

FIGURES 2 and 2A illustrate the separating heater vessel of the invention `showing its basic components; Y

FIGURE 3 is a cross-section View taken along line 3--3 of FIGURE 2.

ICC

Referring to the embodiment of FIGURE l, the vapor generating and turbine installation includes in series an economizer 12, furnace passes 14, and a roof and convection enclosure pass 16. Also constituting sections of the installation are a lpriinary and/ or platen superheating section 13 and `a finishing supierheating section Ztl. During normal operation of the unit, the ilow is through the superheating sections 1S and 20 and from the outlet of the iinishing superheating` section lto a high pressure Yturbine 2 2, the exhaust steam from the turbine being reheatedat 24 and passed to an intermediate pressure turbine't26, a second reheater 2S and a low pressure turbine 30 in that order. From thelow pressure turbine, the iiuid passes to a condenser 32. Being of the oncethrough type, the system ispressurized by a feed pump 34, the uid flowing from the condenser through low pressure heaters 36, deaerator 3S, storage tank 40, high pressure heater 42, separating heater vessel 44 (alternatively by-pass and then to the economizer 12.

Initially in the start-up operation of the steam lgenerator, the feed pump 34 is driven to pressurize the unit upstream of a pressure reducing station 46 (described in copending application, Serial No. 281,452, iiled May 20, 1963) and the liuid How necessary for cooling the high pressure circuitry is established through the unit to the outletof the primary superheater or platen superheate-r 18. One purpose of the reducing station 46 is to maintain normaloperating pressure in the furnace circuitry for adequate cooling of the circuitry, and at the same time, to produce a reduced pressure in the convection surfaces downstream of the reducing station for improved heat transfer in these sections and more rapid start-up. Since the flow during this initial period is entirely liquid, the turbine is incapable of handling the lhow, and accordingly the output from the superheater is by-passed around the turbine and is ffed through stop Ivalve 48 to the separating heater vessel 44. Details of the separating heater will be described funther on. At

this stage, the llow is simply through the vessel draining in line 5t) past valve 52 to the high pressure heater 42 and from there to the deaerator storage tank 40. Valve S4 in the branch 55 of line 5t) leading to the condenser hot well 56 is closed.

To accomplish :by-pass of the start-up mixture from the sufperhcater 18 `to the separating heater, main flow line valve 58 between the platen or primary superheater land 54V (in ylines Sil and 55 leading from the separating g heater 44) maintain an operating pressure of approximately 600 p.s.i. in the separating heater. As soon as some mixture of steam and water starts entering the separating heater 44 from the outlet ofthe pri-mary superheater through valve 4S, the heater functions to separate the steam from the water and to pass the steam to condensing surface within the heater, to be described, where heat is transferred to incoming feedwater.

The condensed steam is removed from the separating heater through line 7) at the bottom of the heater and 'also is directed to the high pressure heater 42 along with the flow from drain 50. In thehigh pressure heater 42, further heat is transferred to the incoming feedwater, thereby avoiding unnecessaryV heat loss.

Upon reaching 4the separating heaters condensing capability any additional steam is directed from the separating heater through line 72 at the top of the heater through proper valves (64, 66, and 68) to different accessories designed to make use of this steam at this time. Included is the deaerator and the turbine gland seals. Some stem is fed to the turbine through valve 62 for warming, rolling and initial loading.

Towards the end of the start-up operation, the steam entering the separating heater may be in the superheat state, and a means for controlling the steam temperature is provided by Way of an attemperator 74.

Once the steam supplied by the generator meets the required conditions for turbine operation, that is, pressure and temperature, the separating heater start-up function is taken out of service by

closing valves

48, 52, 54, 62, 66, and 68, and opening main line Valve 58.

During normal operation of the steam generator, the feedwater to the generator is still directed through the separating heater for preheating prior to entering the economizer 12. Preheating is accomplished by bleeding superheated steam from an intermediate pressure turbine in line 75 and directing it into a desuperheating zone near the bottomof the separating heater. From the de-superheating zone the bleed steam passes thru a condensing zone and then thru a sub-cooling zone. Sub-cooled water is taken out through line 70 near the bottom of the heater and is fed into the high pressure heater 42 for further recovery of available heat.

A better understanding of the invention can be obtained from FIGURES 2, 2A, and 3. Although specific structure is set forth to explain operation of the separating heater and the manner in which it ties in with the steam generator, it is understood that the concepts of the invention are not limited to these specifics. For instance, separating heater orientation could be horizontal or vertical head up, rather than vertical head down as described herein.

FIGURES 2 and 3 show the internal arrangement of the high pressure heater including a xed head 76, a vertical internal channel downcomer 78, an internal separation chamber 80 for steam generator start-up procedure, a condensing section 82, de-superheating section 104, subcooling section 106, and

drain connections

50 and 70. A de-superheating zone and/or a sub-cooling zone are not necessarily required for successful operation of the separating heater.

Heated uid from the furnace and superheating sections Aenter the separating heater tangentially via line 49 into the annular separation chamber. Separation of water and steam occur by centrifugal action. Upon separation, water is thrown to the outside of the annular chamber and collected in a reservoir 92 at the bottom of the chamber. The Water level in the reservoir is' controlled by valves 52 and 54 (FIGURE 1), and is maintained above the drain line 50 and above the bottom edge of the shroud in order to prevent steam from escaping around the bottom edge of the shroud. Any steam obtained in the separation process will rise within the separation chamber 80 and will then flow either downwardly in the downcomer 78into the condensing zone 82 of the heater proper, or upwardly through a secondary means of separation 96. Initially in the start-up cycle, the ow of steam is downwards into the condensing zone 82, wherein the steam will be condensed in surface contact heat exchange with the colder boiler feedwater (entering inlet chamber 114 through conduit i116 and exhausting from chamber 118 to conduit 120) passing through the tubes 9S of the heater. Sub-cooled water is removed at the bottom of the heater through line 70 while saturated water in excess of subcooling zone capacity is removed thru line 108.

An impingement plate 102 is located between downcomer 78 and the condensing tubes 98 in order to prevent any excess moisture in the steam after separation from impinging directly on the tubes.

i The ow of steam to the condensing zone 82 from the separating chamber is achieved as a result of a lower operating pressure in the condensing zone caused by condensation of the high enthalpy uid being cooled by the incoming colder boiler feedwater.

Ultimately in the start-up cycle, the condensing capacity of the tubes 98 is met causing the pressures in the separating chamber and condensing zone to equalize, and steam then will pass upward through the secondary means of moisture elimination, item 96 and then out through line '72 (FIGURE 1). An example of item 96 is a high eiciency centrifugal separator shown in co-pending application Serial No. 107,698, led May 4, 1961. Moisture obtained in this further separation descends outside of the shroud 86 into the reservoir 92.

FIGURE 2A shows the lower portion of the separating heater including the de-superheating and sub-cooling zones 104 and 106 respectively of the heater. Once the start-up system is taken out of service, superheated steam may be bled from an intermediate pressure turbine and admitted in line 75 to the de-superheating zone 104 of the heater proper, for heat conservation. Here the steam transfers its superheat to the incoming feedwater, the de-superheated vapor ybeing transmitted to the condensing zone 82 for transfer of latent heat resulting in condensation of the steam. Saturated water then flows into the subcooling zone 106 for further transfer of heat to the colder feedwater. Sub-cooled waterV is removed through outlet 70. A water level is maintained in the Sub-cooling zone 106 through external instrumentation.

FIGURE 1 illustrates an embodiment of the invention. A by-pass line 110 is provided to by-pass the incoming feedwater around the separating heater. By reducing the amount of feedwater tlowing through the condensing tubes in the heater proper, a much faster pressure stabilization can be obtained between the separating chamber and the condensing zone. This will diminish the condensing capacity of the separating heater, and will result in an earlier production of steam for the accessories mentioned before.

This feedwater by-pass line is optional and is not required or satisfactory operation of the separating heater and the associated start-up system.

It is current Powerplant practice to provide a feedwater heater by-pass line to permit continued unit operation in the event the feedwater heater becomes inoperative. A by-pass line, in accordance with the invention, to provide separating heater outlet steam ow control can be installed for little additional cost to thefstart-up system as compared to this current powerplant practice.

As one advantage, it was mentioned that a greater heat recovery could be achieved in accordance with the invention.

Prior practice has employed a separating vessel and a heat exchange vessel separated by a steam li-ne, and one or more valves. Because of the pressure drop in this line and valves, the saturation temperature in the heat exchanger is less than in the flash tank. Consequently the heat exchanger efficiency is reduced resulting in a lower heat transfer to the feedwater. n

The present invention minimized pressure drop between the separating and heat exchange chambers thus maximizing heat recovered by the feedwater.

In addition, the separating heater is less clostly than a separate flash tank and feedwater heater combination because the former Vessel requires only one fixed head whereas the latter two vessels require three fixed heads. The separating heater permits the start-up system to be simpler and less costly than one employing a separate flash tank and feedwater heater because the steam line connecting the flash tank and feedwater heater is eliminated, together with its one or more valves.

Although the invention has been described with respect to specic embodiments, many variations within the spirit and scope of the invention as defined in the following claims will be apparent to those skilled in the art. For

instance, the separating zone of the heater can be constructed in accordance with the principles set forth in Patent No. 2,675,888, Blizard et al., Vapor and Liquid Separator, with which a horizontally oriented heat exchange zone could be associated.

What is claimed is:

' l. In a once-through vapor generator including heating sections, means for introducing feedwater to said sections, and means for conveying fluid from said sections to points of use,

a start-up system comprising,

an upright cylindrical pressure vessel,

means defining in said vessel an upper first separating zone and a lower second condensing zone,

a partition between said zones defining a central downcomer extending from above the bottom of the first zone to the top of the second zone,

a shroud over and encompassing at least part of the downcomer defining with the downcomer an annular separation zone,

means for tangentially admitting a two-phase uid during start-up from the generator heating sections to said separation zone whereby the two-phase fluid is centrifugally separated into a high enthalpy phase and a low enthalpy phase,

means for transmitting the low enthalpy phase fluid from the separation zone,

means for maintaining a liquid level in the zone above the bottom edge of the shroud, the high enthalpy fluid passing through the downcomer to the second zone,

U-shaped tubes in the second zone,

Vmeans for transmitting the vapor generator feedwater through said tubes in Isurface heat exchange with the high enthalpy fiuid, the cooling effect of the feedwater creating a low pressure inthe second zone relative the pressure in the first zone by which the high enthalpy fluid is drawn into the second zone, the high enthalpy fluid condensing in the zone,

' means for transmitting the condensed high enthalpy f luid from the zone,

said shroud further defining a riser ,above the downcomer, second separation means in said riser,

an outlet in communication with said second separation means,

and means to transmit dry steam from said outlet to points of use operative when the condensing capacity of the U-shaped tubes is met, the pressures in the first and second zones being equal,

said system further having a by-pass for the feedwater around the vessel the use of which permits high enthalpy fluid to be conveyed sooner in the start-up period from said vessel outlet.

2. A once-through vapor-generator comprising:

a main flow path including in series a vapor generating section, a vapor superheating section means adapted to feed all of the ow from the vapor generating section to the superheating section, feedwater means for introducing feedwater to said generating section, means for conveying fluid from said superheating section to a point of use, means for conveying exhaust fluid from said point of use to said feedwater means,

a start-up by-pass system by-passing said point of use comprising,

a pressure vessel including a separating zone and a heat exchange zone,

a first conduit leading from said main flow path downstream of the vapor generating section to said vessel separating zone for conveying a two-phase fluid during start-up of the generator to the separating zone,

separating means in said separating zone for separating the fluid into a high enthalpy phase and a low enthalpy phase,

means Within said vessel leading from said separating zone to the heat exchange zone by which at least a cycling the low enthalpy phase and condensed high v enthalpy phase to the feedwater means,

Vsaid by-pass system further including valve means in said first and second conduits to isolate said by-pass system from the main flow path.

3. A once-through vapor generator comprising:

a main flow path including in series vapor generating and superheating sections, meansadapted to feed allV of the oW from the vapor generating section to the superheating section, feedwater means for introducing feedwater to said generating section, means for conveying fiuid from said superheating section to a point of use, means for conveying exhaust fluid from said point of use to said feedwater means;

a start-up by-pass system by-passing said point of use comprising;

a pressure vessel including a first chamber defining a separating zone and a second chamber defining a heat exchange zone said first chamber having a liquid space and a vapor space,

partition means between said zones defining a passage extending from the vapor space of the first chamber to the heat exchange zone,

a first conduit leading from said main ow path downstream of the vapor generating section to said vessel separating zone for conveying a two-phase fluid during start-up of the generator to the separating zone, said conduit means being adapted to tangentially admit said two-phase fiuid during start-up into the separating zone vapor space in a manner whereby the high enthalpy phase of the fiuid is separated from the low enthalpy phase, the latter iiowing to the liquid space,

heat exchange surface in said second chamber,

means for transmitting the vapor generator feedwater into contact with said heat exchange surface, the condensing affect of said feedwater creating a low pressure in the second chamber by which the high enthalpy phase is drawn through said passage into the second chamber into indirect surface heat exchange with the feedwater,

a second conduit leading from said separating zone vapor space to the main iiow path downstream of the first conduit by which the high enthalpy phase is returned to the main flow path,

third and fourth conduits leading from said separating zone and heat exchange zone, respectively, for recycling the low enthalpy phase and condensed high enthalpy phase to the feedwatermeans,

and valve means in said first and second conduits to isolate said by-pass system from the main flow path.

` 4. A once-through vapor generator according to claim 3, further including means to by-pass feedwater around said heat exchange surface thereby providing high enthalpy fluid sooner in the start-up to said second-conduit. S. A once-through vapor generator according to claim 3 further including separation means in said separating zone between said second conduit and the separating zone vapor space by which dry steam is returned to the main fiow path. l

6. A start-up system according to claim 3 further including a desuperheating zone in said second chamber,

baiiie means separating the desuperheating zone from said heat exchange surface,

means for transmitting a superheated phase uid from said points of use to the desuperheating zone,

further heat exchange surface in the desuperheated zone whereby the fluid is desuperheated,

means for transmitting the desuperheated uid from the desuperheating zone to direct contact with the rst mentioned heat exchange condensing surface, the Huid condensing on said condensing surface,

said further condensing heat exchange surface being an extension of said first mentioned desuperheating zone heat exchange surface.

References Cited by the Examiner UNITED STATES PATENTS 2,756,028 7/56 Byeney 165-415 2,982,102 5/61 Protos a 60-107 5 3,008,295 11/61 Profos 60-107 3,009,525 11/61 Pirsh 122-1 PERCY L. PATRICK, Primary Examiner.

10 KENNETH W. SPRAGUE, Examiner.

Claims

2. A ONCE-THROUGH VAPOR-GENERATOR COMPRISING: A MAIN FLOW PATH INCLUDING IN SERIES A VAPOR GENERATING SECTION, A VAPOR SUPERHEATING SECTION MEANS ADAPTED TO FEED ALL OF THE FLOW FROM THE VAPOR GENERATING SECTION TO THE SUPERHEATING SECTION, FEEDWATER MEANS FOR INTRODUCING FEEDWATER TO SAID GENERATING SECTION, MEANS FOR CONVEYING FLUID FROM SAID SUPERHEATING SECTION TO A POINT OF USE, MEANS FOR CONVEYING EXHAUST FLUID FROM SAID POINT OF USE TO SAID FEEDWATER MEANS, A START-UP BY-PASS SYSTEM BY-PASSING SAID POINT OF USE COMPRISING, A PRESSURE VESSEL INCLUDING A SEPARATING ZONE AND A HEAT EXCHANGE ZONE, A FIRST CONDUIT LEADING FROM SAID MAIN FLOW PATH DOWNSTREAM OF THE VAPOR GENERATING SECTION TO SAID VESSEL SEPARATING ZONE FOR CONVEYING A TWO-PHASE FLUID DURING START-UP OF THE GENERATOR TO THE SEPARATING ZONE, SEPARATING MEANS IN SAID SEPARATING ZONE FOR SEPARATING THE FLUID INTO A HIGH ENTHALPY PHASE AND A LOW ENTHALPY PHASE, MEANS WITHIN SAID VESSEL LEADING FROM SAID SEPARATING ZONE TO THE HEAT EXCHANGE ZONE BY WHICH AT LEAST A PORTION OF THE HIGH ENTHALPY PHASE IN CONVEYED TO THE HEAT EXCHANGE ZONE, A SECOND CONDUIT LEADING FROM SAID SEPARATING ZONE TO THE MAIN FLOW PATH DOWNSTREAM OF THE FIRST CONDUIT BY WHICH AT LEAST ANOTHER PORTION OF THE HIGH ENTHALPY PHASE IS RETURNED TO THE MAIN FLOW PATH, MEANS IN THE HEAT EXCHANGE ZONE BY WHICH SUFFICIENT LATENT HEAT IN THE HIGH ENTHALPY PHASE IS TRANSFERRED TO THE VAPOR GENERATOR FEEDWATER TO CONDENSE THE HIGH ENTHALPY PHASE, THIRD AND FOURTH CONDUITS LEADING FROM SAID SEPARATING ZONE AND HEAT EXCHANGE ZONE, RESPECTIVELY, FOR RECYCLING THE LOW ENTHALPY PHASE AND CONDENSED HIGH ENTHALPY PHASE TO THE FEEDWATER MEANS, SAID BY-PASS SYSTEM FURTHER INCLUDING VALVE MEANS IN SAID FIRST AND SECOND CONDUITS TO ISOLATE SAID BY-PASS SYSTEM FROM THE MAIN FLOW PATH.